The instant invention pertains to a superior process for making 2H-benzotriazole UV absorbers which are substituted by a perfluoroalkyl group, i.e. trifluoromethyl, usually at the 5-position of the benzoic ring; and to a novel process for the preparation of the intermediate 2-(2-nitophenylazo) phenols.
Japanese TOKU-KAI-Hei 3-57690 generically discloses compounds where the benzoic ring of the benzotriazole may be substituted by a host of groups including hydrogen, alkyl, alkoxy, aryloxy, halogen, substituted amino, cyano, nitro, acyl and trihalomethyl. The only specific benzotriazole compounds mentioned are those where the benzoic ring is unsubstituted or is substituted at the 5-position by a chloro group. There is no evidence that the Japanese inventors made any trihalomethyl substituted benzotriazole.
German Patent Application 116,230 describes inter alia the preparation of 5-trifluoromethyl-2-(2-hydroxy-5-methylphenyl)-2H-benzotriazolyl-1-oxide. The only synthesis conditions disclosed for the entire group of compounds prepared show the diazotization of the appropriate o-nitroaniline with aqueous sodium nitrite and hydrochloric acid. The German workers offer no synthetic details or more importantly no yield information for the preparation of 5-trifluoromethyl-2-(2-hydroxy-5-methylphenyl)-2H-benzotriazolyl-1-oxide.
In British Patent Application 2,319,035 and U.S. Pat. No. 5,977,219, all benzotriazole compounds containing a trifluoromethyl moiety at the 5-position of the benzoic ring are referenced to the synthetic procedure of Example 1. Issues to be considered with this synthetic procedure are (a) a 100% excess of the diazonium salt relative to phenol is used; (b) the monoazo prepared by this method is described as a paste (generally materials with the consistency of a paste are impure); the pure monoazo is a solid with a melting point of 101-105xc2x0 C.; (c) the yield of benzotriazole based on the phenol is 11% and is only 5.5% based on the CF3-substituted o-nitroaniline; (d) the diazotization preparation in Example 1 uses concentrated hydrochloric acid; (e) a paper in the J. Org. Chemistry, 1985, (50) 3612 indicates that the reaction of 4-trifluoromethyl-2-nitroaniline with hydrochloric acid can lead to the formation of 4-trifluoromethyl-2-chloroaniline. Such a reaction could at least partly account for the low yields seen with the use of concentrated hydrochloric acid in the diazotization step.
The following references describe one-pot processes for making azo compounds:
U.S. Pat. No. 2,418,416 describes a process for manufacturing lakes of azo compounds. The process involves dissolving the diazotizable amine and coupling component in an acidic, aqueous solution. The amine was diazotized by addition of the nitrosating reagent to the acidic, aqueous solution. After diazotization was complete, the pH of the solution was raised by addition of base to ca. 7.8.
U.S. Pat. No. 2,478,767 also describes a process for manufacturing lakes of azo compounds. The diazotizable amine is dissolved in an acidic, aqueous solution and heated to 100xc2x0 F. The coupling component and nitrosating reagent are dissolved in a basic, aqueous solution that is heated to 150xc2x0 F. The two solutions are mixed together controlling the pH of the mixture in the range of 6-7.2.
U.S. Pat. No. 2,478,768 also describes a process for manufacturing lakes of azo compounds. The process involves adding an acidic, aqueous solution containing a soluble salt of the laking agent to a basic, aqueous solution containing the diazotizable amine, coupling component and nitrosating reagent. The final pH of the reaction mass is 6-7.2.
U.S. Pat. No. 3,793,305 describes a one-step process for the preparation of azo dyes by simultaneously contacting and reacting a diazotizable amine, an active methylene coupling component and a digitizing agent in an acidic, aqueous solution. The invention requires that the reaction media must be able to dissolve a portion of both the diazotizable amine and the coupling component. The active methylene coupling components named are: b-diketones, b-keto esters, b-keto amides, b-keto nitrites, anilides of cyanoacetic acid, heterocyclic b-keto amides and b-imino amides.
U.S. Pat. No. 4,035,350 describes a process for the preparation of azo dyes where the diazotizable amine and the coupling component are both in solution and the digitizing agent is added. The invention requires that either the amine or coupling component contain an acid group. The invention also claims the use of polar aprotic solvents that are miscible with water.
Hashida, Y. et. al. reported in xe2x80x9cPhase Transfer-Catalyzed Azo Coupling Reaction in Two Phase Systemsxe2x80x9d, Bull. Chem. Soc. Jpn. 61, 905-909 (1988) the phase transfer catalyzed azo coupling reaction in a two phase system. This paper describes the coupling reaction between p-methoxybenzenediazonium tetrafluoroborate with N,N-dimethylaniline in a biphasic water-1,2-dichloroethane system with various phase transfer catalysts.
Tamagaki, S. et. al. reported in Chemistry Letters, pp. 1237-1240 (1982) for the Chemical Society of Japan that silica gel facilitated azo coupling reactions between p-nitrobenzenediazonium tetrafluoroborate and aromatic amines. This process involves a solid-solid-liquid multiphase mixture via a solid-liquid interfacial azo-coupling reaction.
In March, J, xe2x80x9cAdvanced Organic Chemistry,xe2x80x9d Fourth Ed., New York, pages 522-523, it is pointed out that it is well known that active substrates such as phenols are readily nitrated under standard nitrosation conditions.
An object of the invention is to provide a facile and improved process for the preparation of 5-perfluoroalkyl substituted 2H-benzotriazole UV absorbers.
Another object of the invention is to provide a novel one-pot process for the preparation of 2-(2-nitrophenylazo) phenols, referred to in this application as monoazobenzene intermediates. These monoazobenzene intermediates are useful for the preparation of hydroxyphenyl benzotriazole UV absorbers.